* {
    margin: 0;
}

/* 元素选择器 */
body {
    height: 100vh;
}

header {
    height: 20%;
}

main {
    height: 60%;
}

footer {
    background-color:#0000ff;
    height: 20%;
}

nav {
    float: right;
    padding-top: 10px;
}

nav a {
    margin-right: 10px;
    color: #333;
    font-weight: 700;
    line-height: 24px;
    font-size: 13px;
    text-decoration: underline;
}

form {
    text-align: center;
}

.search-box {
    width: 539px;
    height: 34px;
}


.btn-submit {
    width: 100px;
    height: 40px;
    background-color: #3385ff;
    border: none;
    margin-left: -5px;
}

.img-logo {
    width: 270px;
    height: 129px;
    margin-bottom: 10px;
}

.block-ele {
    background-color: green;
    width: 200px;
    margin-left: auto;
    margin-right: auto;
}